Dyntopo destroying mesh when scultping
Dyntopo dynamically changes your mesh topology as you sculpt. It looks like you have collapsed the mesh detail in the chest area, maybe while zoomed out.

The settings that control how your mesh is altered are the detail size, the refine method and the detailing type.


The detail size determines how long any mesh edge should be.
The detailing type determines what measurement to use.


Relative detail is based on screen pixels, as you zoom in and out the size of the edges changes.
Constant detail is based on blender units, keeping the same size as you zoom in and out.
Brush detail is based on the size of your brush, resizing the brush changes the detail size.

The refine method determines what action to take.


Subdivide edges will only add new edges to achieve the detail you want.
Collapse edges will only remove excess edges that are not needed for the detail level you are after.
Subdivide Collapse will dynamically add or remove edges.



Note that each detail type uses a different type of measurement, changing this can lead to different levels of detail, with only constant detail offering an eyedropper to set the value to match an area of your mesh.

While you are unfamiliar with dyntopo, I would recommend keeping the refine method to subdivide unless you specifically want to reduce the detail. By using subdivide collapse it is too easy to remove detail while you are zoomed out for an overall appraisal.